Volume control



D. P. EARNSHAW VOLUME CONTROL Filed Oct.

Mmh 2, 1937.

L-oc; e7 0% 7"} g; 46 5475 my Patented Mar. 2, 1937 UNITED STATES PATENT OFFICE to Philco Radio & Television Corporation,

Philadelphia, Pa., a corporation of Delaware Application October 28, 1935, Serial No. 47,151 In Great Britain October 29, 1934 9 Claims.

This invention relates to volume control for radio receivers and like systems employing a plurality or series of vacuum tubes or space discharge devices in cascade arrangement. The object of the invention is to provide a novel means for controlling the operation of successive vacuum tubes to control thereby the output signal level of the system. This object is achieved by the provision of a common variable source of biasing potential from which biasing voltages are applied to successive vacuum tubes in conjunction with means for varying the amplitude of the incoming signal applied to the receiver, and by using the same means to prevent overloading of one or more of the controlled stages.

The invention may be understood from the following description of the specific embodiments illustrated in the accompanying drawing.

In the drawing:

Fig. 1 is a diagrammatic illustration of a portion of a radio receiver embodying the biasing method of the invention; and

Fig. 2 is a similar illustration of a modification.

While the invention is applicable to any group of successive vacuum tube stages, regardless of the specific functions of the stages, for the purpose of illustration, the invention may be considered as applied to three vacuum tube stages of a superheterodyne radio receiver. Thus, in

Fig. 1 of the drawing, the first vacuum tube stage V1 may be a detector-oscillator, the oscillator section being omitted for simplicity of illustration, the second vacuum tube stage V2 may be an intermediate frequency amplifier, and the third vacum tube stage V3 may be the second detector operating as an anode-bend detector.

As shown in Fig. 1, there is provided in the antenna circuit of the radio receiving system, a potentiometer P and a source of unidirectional potential B, which may be a battery, serially connected as illustrated. One extremity of the potentiometer P is connected to the antenna A preferably through a blocking condenser, while the other extremity of the potentiometer is connected to the negative side of source B. The positive side of source B is connected to ground, as illustrated. If desired, a high frequency by-pass condenser may be shunted about source B.

The adjustable tap of the potentiometer P is connected to one extremity of the primary windin of input transformer T1, the other extremity of the primary winding being connected to ground through a resistor R. One extremity of the secondary winding of transformer T1 is connected to 55. the control electrode of the vacuum tube of stage V1 while the other extremity of the secondary winding is connected to resistor R and to the bypass condenser C shunted about the resistor.

It will be seen that unidirectional current will flow through the loop circuit comprising that part 5 of the potentiometer from the adjustable tap to source B, the said source, resistor R, and the primary winding of the input transformer T1. A unidirectional voltage will, therefore, be set up across resistor R having the polarity indicated. 10 The negative end of resistor R, as established by the said voltage, is connected through a filter resistor R1 to an extremity of each of the secondary windings'of coupling transformers T2 and T3, the other extremity of each of the secondary windings 15 being connected to the control electrode of the vacuum tube associated therewith. The cathodes of all of the vacuum tubes may be connected to a common ground lead, as illustrated.

It will be seen that the resistor R is included in 20 the input circuit of each of the vacuum tubes and that the resistor R1 is additionally included in the input circuits of the vacuum tubes of stages V2 and V3. It will also be seen that the voltages across the resistors serve to bias the tubes. The 25 adjustment of potentiometer P determines the biasing voltage available across resistor R. With the potentiometer adjusted so that all of its resistance is out of the loop circuit above mentioned, the entire unidirectional voltage drop in the loop 30 circuit will be across resistor R, so that the full biasing voltage will be available at such time across resistor R. With the potentiometer adjusted so that all of its resistance is included in the loop circuit, however, the voltage drop across 35 resistor R will be considerably less. For intermediate adjustments of the potentiometer, the biasing voltage available across resistor R will vary accordingly. At the same time, adjustment of the potentiometer varies the amplitude of the 40 signal modulated carrier wave applied to the system, since the entire signal from the antenna will appear across the potentiometer but only that portion of the signal between the adjustable tap and ground will be transferred to the input 45 transformer T1.

It will be seen that various biasing potentials of the full adjustable range of values may be applied simultaneously to all three of the vacuum tubes by manipulation of the potentiometer P, 50 the negative biasing voltage across resistor R increasing as the incoming signal is reduced by adjustment of the potentiometer. This increase in biasing potential serves, of, course, to reduce the amplification of the stages by rendering the control grids of the tubes more negative with respect to their cathodes. The proper bias is also supplied to the anode-bend detector whose sensitivity is a function of the bias. By proper design, the detector may be made most sensitive for weak signals but less sensitive for strong signals where the bias is increased. The controllable bias serves moreover to increase the overload point of the last tube which, in the illustrated system, is a second detector of the anode-bend type. As long as no overloading occurs, there will be no flow of grid current in the input circuits of. the tubes and there will, therefore, be no current flow through the resistor R1 and no voltage dropthereacross.

If, however the last tube overloads, as it will before overload occurs elsewhere, grid current will flow through the input circuit of the tube and through the resistor R1, thereby causing a voltage drop across that resistor which increases with the amount of overloading. The circuit is so arranged that the negative side of the resistor R1 as determined by the polarity of the voltage drop, is connected to the control grids of the last two tubes, so that the voltage drop across the resistor places an additional negative bias on the last two tubes. The first tube is also automatically biased to some extent at least by the voltage drop across the resistor R. This action will increase as the value of resistor R is increased relative to the value of the resistor R1.

In Fig. 2, there is illustrated a modified form of the invention in which there is provided a branch circuit connected between the secondary F winding of transformer T3 and the cathode of the last tube. This branch circuit may include a source of unidirectional voltage B1, arranged so as to apply a negative bias to the controlgrid of the last tube, and a resistor R2 serially connected with the said source. The effect of this arrangement is to prevent application to the last tube of the full increase in biasing voltage ob tained by adjustment of. potentiometer P. This results from the drop in voltage which is normally present across resistor R1 due to the flow of ourrent therethrough during various adjustments of the potentiometer.

By this modification, the bias on thelast stage, which may be a biased detector, may be more critically determined.

The various elements above described may be given any suitable values which may be desired in any particular instance. A specific example of the values of the various elements which may be employed is as follows: The potentiometer P may have a resistance of 20,000 ohms, the voltage of. the unidirectional voltage source B may be 7.5 volts, and the resistance of resistor B may be 13,000 ohms. These values give a range of. voltage across the resistor R from 3 volts minimum to 7.5 volts. maximum. The resistance of the filter resistor R1 may be 0.1 mcgohms, while the value of the resistor R2 may be 0.5 ,megohms. The unidirectional voltage source B1 may be a source of 3 volts.

It will be seen that the invention embodies certain novel features and accomplishes certain desirable results which may be summarized as follows:

First, the potentiometer varies the amplitude of the incoming radio frequency energy applied to the receiving system. At the same time, the potentiometer varies the amplitude or value of the biasing voltage produced across the resistor R.

Second, a variable biasing control is applied to any or all of. the successive tubes, thereby efiecting volume control by variation of the amplification of the successive stages.

Third, the overload point of the last tube is X' tended by the bias, and when overload does ocour, the bias on several of the tubes is automatically increased by the same means which provide the second result.

Although the invention has been illustrated and described with reference to certain specific forms, it will be understood that it is not thus limited and is capable of various modifications. Moreover, the number of stages to which the invention is applied in any instance may be varied. For example, one or more stages may be cooperatively connected to stage V1 in the manner of stages V2 and V3 so as to supply the desired variable bias voltage thereto. It will be understoodof course that vacuum tubes of any desired type may be used, the tubes being illustrated as triodes merely for the sake of simplicity. Other such modifications will occur to persons skilled in the art.

I claim:

l. Ina radio receiver; a space discharge device having a control element; a signal collecting device; means, including resistance means having a variable portion and a source of unidirectional potential, for varying the portion of signal transferred from said signal collecting device to said space discharge device and for varying the unidirectional potential across part of said resistance means; connections between said resistance means and said space discharge device to bias said control element of said device;

at least one other space discharge device having I a control element; and biasing means for said other space discharge device, including a resistor connected to said part of said resistance means and another resistor and a source of unidirectional potential connected to said part of said resistance means and to said first resistor.

2. In a radio receiver; a space discharge device having'a control element; a signal collecting device; means, including resistance means having a variable portion and a source of unidirectional potential, for varying the portion of signal transferred from said signal collecting device to said space discharge device and for varying the unidirectional potential across part of said resistance means; connections between said resistance means and said space discharge device to bias said control element of said device; at least one other space discharge device, including an anodebend detector having a control element; and biasing means for said other space discharge device, including a resistor connected to said part of said resistance means and another resistor and a source of unidirectional potential connected to said part of said resistance means and to said first resistor.

3. In a radio receiver; a space discharge device having a control element; a signal collecting device; means, including resistance means having a variable portion and a source of unidirectional potential, for varying the portion of signal transferred from said signal collecting device to said space discharge device and for varying the unidirectional potential across part of said resistance means; connections between said resistance means and said space discharge device to bias said control element of said device; a plurality of other space discharge devices having control elements, one of said other space discharge devices being an anode-bend detector; and biasing means for said other space discharge devices, including conductive means connected to said control elements, a resistor connected to said conductive means and to said part of said resistance means, and another resistor and a source of unidirectional potential connected to said part of said resistance means and to said conductive means.

4. In a radio receiver, a space discharge device having a cathode and a control element, a signal source, means for selecting a variable portion of the signal and transferring it from said signal source to said space discharge device, and for varying the unidirectional potential of said control element with respect to said cathode, comprising a variable resistance, a second resistance, and a source of unidirectional potential having negative and positive terminals, connected in series relation to form a circuit conductive to unidirectional currents, said variable resistance being connected to said negative terminal, and said second resistance being connected to said positive terminal, connections to apply signals from said source to said variable resistance, a connection conductive to unidirectional currents from said control element to said series circuit between said resistances, and a connection conductive to unidirectional currents from said cathode to said source of unidirectional potential.

5. In a radio receiver, a space discharge device having a cathode and a control element, a signal source, means for selecting a variable portion of the signal and transferring it from said signal source to said space discharge device, and for varying the unidirectional potential of said control element with respect to said cathode, comprising a potentiometer including a resistance and a variable connection to a portion of said resistance, a second resistance, and a source of unidirectional potential having negative and positive terminals connected in series relation with said second resistance and said portion of said first resistance to form a circuit conductive to unidirectional currents, said potentiometer being connected to said negative terminal, and said second resistance being connected to said positive terminal, connections to apply signals from said source to said potentiometer, a connection conductive to unidirectional currents from said control element to said series circuit between said resistances, and a connection conductive to unidirectional currents from said cathode to said source of unidirectional potential.

6. In a radio receiver, a space discharge device having a cathode and a control element, a signal source, means for selecting a variable portion of the signal and transferring it from said signal source to said space discharge device, and for varying the unidirectional potential of said control element with respect to said cathode, comprising a variable resistance, a second resistance, and a source of unidirectional potential having negative and positive terminals, connected in series relation to form a circuit conductive to unidirectional currents, said variable resistance being connected to said negative terminal, and said second resistance being connected to said positive terminal, connections to apply signals from said source to said variable resistance, a conneotion conductive to unidirectional currents from said control element to said series circuit between said resistances, a connection conductive to unidirectional currents from said cathode to said source of unidirectional potential, at least one other space discharge device having a cathode and a control element, a connection conductive to unidirectional currents from said lastnamed cathode to said source of unidirectional potential, and a connection conductive to unidirectional currents and including a resistance from said last-named control element to said series circuit between said resistances.

7. In a radio receiver, a space discharge device having a cathode and a control element, a signal source, means for selecting a variable portion of the signal and transferring it from signal source to said space discharge device, and for varying the unidirectional potential of said control element with respect to said cathode, comprising a potentiometer including a resistance and a variable connection to a portion of said resistance, a second resistance, and a source of unidirectional potential having negative and positive terminals connected in series relation with said second resistance and said portion of said first resistance to form a circuit conductive to unidirectional currents, said potentiometer being connected to said negative terminal, and said second resistance being connected to said positive terminal, connections to apply signals from said source to said potentiometer, a connection conductive to unidirectional currents from said control element to said series circuit between said resistances, a connection conductive to undirectional currents from said cathode to said source of unidirectional potential, at least one other space discharge device having a cathode and a control element, a connection conductive to unidirectional currents from said last-named cathode to said source of unidirectional potential, and a connection conductive to unidirectional current and including a resistance from said lastnamed control element to said series circuit between said resistances.

8. In a radio receiver, a space discharge device having a cathode and a control element, a signal source, means for selecting a variable portion of the signal and transferring it from said signal source to said space discharge device, and for varying the unidirectional potential of said control element with respect to said cathode, comprising a variable resistance, a second resistance, and a source of unidirectional potential having negative and positive terminals, connected in series relation to form a circuit conductive to unidirectional currents, said variable resistance being connected to said negative terminal, and said second resistance being connected to said positive terminal, connections to apply signals from said source to said variable resistance, a connection conductive to unidirectional currents from said control element to said series circuit between said resistance, a connection conductive to unidirectional currents from said cathode to said source of unidirectional potential, a plurality of space discharge devices each having a cathode and a control element, a connection conductive to unidirectional currents from said last-named cathodes to said source of unidirectional potential, and a connection conductive to unidirectional currents and including a resistance from said last-named control elements to said series circuit between said resistances.

9. In a radio receiver, a space discharge device having a cathode and a control element, a signal source, means for selecting a variable portion of the signal and transferring it from said signal source to said space discharge device, and for varying the unidirectional potential of said control element with respect to said cathode, comprising a potentiometer including a resistbetween said resistances, a connection conductive to unidirectional currents from said cathode to said source of unidirectional potential, a plurality of space discharge devices each having a cathode and a control element, a connection conductive to 5 unidirectional currents from said last-named cathodes to said source of unidirectional potential, and a connection conductive to unidirectional currents and including a resistance from said last-named control elements to said series 10 circuit between said resistances.

DAVID P. EARNSHAW. 

